In the cholera vaccine trial discussed in [1]}, [2]}, [3]}, [4]}, participants were randomized between receiving the vaccine or placebo. Participation rates – and hence vaccination rates as well – varied widely across neighborhoods, and better outcomes for both treated and control were observed in neighborhoods where vaccination rates were high. These trends suggest that each unit's outcome was not only affected by their own vaccination status, but was also affected by the vaccination status of others as well. Evidence of interference was also found between neighborhoods, through shared bodies of water and kinship ties such as marriage [4]}.
